The present disclosure relates generally to image processing and, more particularly, to generating a high dynamic range (HDR) tone mapped, high-local-contrast image in an electronic device.
This section is intended to introduce the reader to various aspects of art that may be related to various aspects of the present techniques, which are described and/or claimed below. This discussion is believed to be helpful in providing the reader with background information to facilitate a better understanding of the various aspects of the present disclosure. Accordingly, it should be understood that these statements are to be read in this light, and not as admissions of prior art.
Electronic devices increasingly employ cameras or other image capture devices. For example, handheld devices such as portable phones and portable media players increasingly use cameras to capture images and video. Even notebook and desktop computers may routinely include front-facing cameras and/or other image capture devices, allowing a user to easily generate user profile photographs and/or capture video for video conferencing. These image capture devices may capture image data of a bit depth higher than the data paths commonly used for image signal processing. Some image capture devices may capture image data with a bit depth exceeding 10 bits, for example, while image signal processor data paths may typically use image data of only 8 bits. In addition, many compression methods (e.g., MPEG, JPEG, and/or H.264) generally involve processing 8-bit image data. Accordingly, image data from image capture device may be compressed from a higher bit depth to a lower bit depth before reaching an image signal processor core, where most hardware image signal processing may take place. Reducing the bit depth of the image data from a higher bit depth (e.g., 10-14) to a lower bit depth (e.g., 8) may result in a loss of details as the dynamic range that can be described by the lower bit depth decreases correspondingly. Indeed, dynamic ranges within images will generally exceed the range of 8 bits, even though 8 bits may almost be sufficient to smoothly render a uniformly lit surface. However, shadows and specular highlights can easily require 14-16 bits to capture the full dynamic range of a scene.
Typically, the loss of dynamic range that occurs when higher-bit-depth image data is reduced to lower-bit-depth image data is mitigated by applying a transfer function. The transfer function may map the higher-bit-depth image data to lower-bit-depth image data in a manner that may be indistinguishable to the human eye over much of the original dynamic range. However, such image data compression may clip some highlights and/or shadows originally represented in the higher-bit-depth image data.
Various techniques have thus been developed for obtaining an image that appears to include all of the details of a higher-bit-depth, high dynamic range (HDR) image despite having a relatively low bit depth. Conventionally, these HDR techniques involve capturing multiple images at various levels of light exposure. Typically, at least one such image contains specular highlight details and at least one contains shadow details. Combining properly exposed portions of these multiple images into a single image may produce an image that includes both highlights and shadows. However, obtaining such an HDR-tone-mapped image in this manner may be memory and/or processor intensive, drawing additional power and reducing the efficiency of an electronic device. Moreover, because such HDR image processing may require multiple images taken at different exposure times, it may be difficult or impossible to obtain an HDR-tone-mapped image when an image involves a moving subject.